Native Gantt (Preview) vs Custom Gantt in Power BI: When You Still Need a Custom Visual

The Gantt visual is a preview feature. Learn's What's new entry for October 2026 says to "enable the visual under Preview features in Desktop and restart Desktop to try it". Preview features live under File, Options and settings, Options; tick the Gantt entry there. After the restart it appears in the Visualizations pane like any core visual. Learn does not yet say how the preview behaves in the Power BI service, so test a published report before you rely on it there.

Fields: "The only required field is the label for each row or task." Start and End give duration bars; "for milestones, provide a start date and leave End blank". Start and End "can both use measures", which lets you control how dates aggregate at category levels and return a blank End to turn a row into a milestone.

Progress: "add a measure that calculates each row's percentage complete", then format how it appears, including "the percentage of the bar's height that the progress indicator occupies", as a transparent white overlay or as a fill inside an outlined bar.

Grouping: "Add up to three levels of categories to group tasks."

Columns: "Add columns next to the task list to show details like owner, status, or duration." Subtotals at category levels require measures or aggregations. Columns can be styled per level, links can render as icons, and the column area auto-sizes or takes a fixed width with a scrollbar when columns overflow.

Colour: Rows > Color sets one colour that "cascades to categories, task bars, milestones, and row backgrounds" with documented default transparencies (task bars 0%, first-level category background 70%, second 80%, third 90%, task rows 100%). "More granular" switches a level to data colours, and "conditional formatting is also available."

Axis: set the displayed start and end dates; Auto-scale switches a single level between years, months and days; with Auto-scale off, choose up to two fixed levels (for example months over years) with custom display formats; shade chosen weekdays.

Zoom: "The zoom axis feature helps report readers focus on a specific calendar window and then return to the full range."

Limits, quoted: "The Gantt visual supports up to 1,000 rows." "Auto-scale doesn't display levels more granular than days", though bars can represent partial days. Measure display formatting "might not appear in tooltips or columns"; the workaround is the Data format option on the General tab.

This section is deliberately phrased as "not mentioned", not "not supported". The documented feature list contains no reference to:

Dependencies or predecessor links: no arrows between tasks, no finish-to-start relationships.

Critical path highlighting.

Baselines: no second bar per task for planned versus actual.

Drag-to-edit or write-back: dates come from the model and the visual is read-only.

Resource or capacity lanes, or a resource histogram.

Row counts above 1,000, which is an explicit limit.

Auto-scale finer than days, also explicit.

If one of these is a requirement, test the current preview build before assuming a gap, because preview features gain capabilities month to month. If the gap is confirmed, you are in custom-visual territory.

Most project status pages. A roadmap or release calendar with phases, tasks, milestones and percent complete is exactly the documented sweet spot: three grouping levels, progress fills, milestones from a blank End measure, weekend shading, and a zoom control for the quarter in focus. The native visual also inherits what custom visuals have to earn: it is a core visual (no tenant policy to negotiate), it is formatted from the same format pane and theme as the other built-in visuals (test cross-filtering with your slicers while it is in preview), and it should work in Publish to web and Report Server once it leaves preview and reaches those surfaces. If your old Gantt was a marketplace visual with a per-user licence doing only this, switching saves money and governance effort.

1. Dependencies and critical path. Project managers read a Gantt by its arrows. A custom visual computes the longest path from a predecessor column and highlights it; the native visual, as documented, does not draw links.
2. Baselines. Planned versus actual as two bars per row, with slip shown as a gap, is a core portfolio-review view. It needs a second Start/End pair per task.
3. Scale. Portfolios with more than 1,000 tasks, or construction schedules that need hour-level bars with a visible hour axis, exceed the documented limits.
4. Interaction beyond filtering. Drag a bar to propose a new date and write it back through Power Apps or a form endpoint, collapse and expand groups with remembered state, or jump to the current week with a button inside the visual.
5. Specific rendering. Swimlanes by resource with capacity shading, custom milestone glyphs, labels inside bars, a today line with an offset, a print layout for an A3 plan.
6. Your own formatting pane. Teams that standardise on one Gantt across many reports want the formatting cards named for their process, not generic.

A marketplace Gantt covers several of these for a per-user fee. A generated .pbiviz covers the ones you specify, once, with source code you keep; it is uncertified, so your tenant must allow SDK visuals.

Put the native preview and your candidate custom Gantt on the same page, bound to the same table (Task, Start, End, Percent Complete, Phase, Owner, Predecessor). Then walk the checklist with a project manager:

1. Milestones render where End is blank in both.
2. Progress reads the same percent and the same visual encoding.
3. Three-level grouping collapses the way they expect.
4. Dependencies: visible in the custom visual, confirm absence or presence in the native build you have.
5. Baseline: same test.
6. Row count: load the full portfolio and watch the 1,000-row limit.
7. Tooltips and columns show formatted measures (apply the Data format workaround on the native visual).
8. Export to PDF and open in the mobile app.

If the native visual passes every row that matters to your readers, use it. The custom visual earns its place on the rows it fails.

Whether you brief a developer, pick a marketplace visual or prompt a generator, write the requirement as data roles and behaviours, not as a picture. For example: "Data roles: Task (text), Start (date), End (date), Percent Complete (measure), Phase (category, two levels), Predecessor (text, comma-separated task IDs), Baseline Start, Baseline End. Draw dependency arrows finish-to-start, highlight the critical path in the theme's first data colour, show baseline as a thin bar under the actual bar, today line, collapse groups on click, cross-filter on bar click, tooltip with slip in days, formatting pane cards for bar colours, arrow style, baseline visibility and date format." That brief maps directly to capabilities.json data roles and formatting cards, which is what a .pbiviz is.